Guest post by BHodges.
Discourse by Brigham Young
March 16, 1856
On March 14, 1856 Brigham Young addressed a group of Saints at the Social Hall where he told the congregation “think, brethren, think, but do not think so far that you cannot think back again.” Two days later he resumed the thought in his address at the Tabernacle, urging his listeners to develop balance:
In the eastern country there was a man who used to go crazy, at times, and then come to his senses again. One of his neighbors asked him what made him go crazy; he replied, “I get to thinking, and thinking, until finally I think so far that I am not always able to think back again.”
Can you think too much for the spirit which is put in the tabernacle?
You can, and this is a subject which I wish the brethren instructed upon, and the people to understand. The spirit is the intelligent part of man, and is intimately connected with the tabernacle. Let this intelligent part labor to excess, and it will eventually overcome the tabernacle, the equilibrium will be destroyed, and the whole organization deranged. Many people have deranged themselves by thinking too much.
Brigham was encouraging moderation in all things, including study and critical thinking.
During the translation of the Book of Mormon, the Lord cautioned the perhaps exuberant Joseph Smith to avoid over-exertion:
Do not run faster or labor more than you have strength and means provided to enable you to translate; but be diligent unto the end (D&C 10:4).
A similar warning is found within the Book of Mormon itself; as King Benjamin admonished:
And see that all these things are done in wisdom and order; for it is not requisite that a man should run faster than he has strength. And again, it is expedient that he should be diligent, that thereby he might win the prize; therefore, all things must be done in order (Mosiah 4:27).
Brigham preached of a well-rounded routine, with both mental and physical conditioning:
The thinking part is the immortal or invisible portion, and it is that which performs the mental labor; then the tabernacle, which is formed and organized for that express purpose; brings about or effects the result of that mental labor. Let the body work with the mind, and let them both labor fairly together, and, with but few exceptions, you will have a strong-minded, athletic individual, powerful both physically and mentally.
When you find the thinking faculty perfectly active, in a healthy person, it should put the physical organization into active operation, and the result of the reflection is carried out, and the object is accomplished. In such a person you will see mental and physical health and strength combined, in their perfection. We have the best opportunity afforded any people to cultivate these properties of man.
One of the reasons Brigham had the Social Hall built was to allow the people some entertainment and culture aside from the drudgery of everyday work and from study. He believed we need an outlet, lest we become machines:
When a person is thinking all the time he is little better than a machine; he perverts the purpose of his organization, and injures both mind and body.
Why? Because the mental labor does not find vent through the organism of the tabernacle, and has not that scope-that field of labor which it desires, and which it was wisely designed that it should have. Think according to your labor, labor according to your thinking.
Joseph Smith is said to have acted on a similar principle. John W. Hess related a time in 1838 when the prophet stayed at his father’s house for a few weeks:
At that time Joseph was studying Greek and Latin. When he got tired studying, he would go and play with the children in their games about the house, to give him exercise. Then he would go back to his studies. 
Some think too much, others labor too much; Brigham encouraged moderation:
Some think too much, and should labor more, others labor too much, and should think more, and thus maintain an equilibrium between the mental and physical members of the individual; then you will enjoy health and vigor, will be active, and ready to discern truly, and judge quickly.
Is it not your privilege to have discernment to circumscribe all things, no matter what subject comes before you, and to at once know the truth concerning any matter? When you see a person of this character, you see one with a healthy and vigorous mind, throughout the whole operations of organization. True, this is not the privilege of every one; some have to do much thinking, and but little manual labor, while others do much manual labor with little, if any thinking.
The latter class are as dull and stupid as the brutes, and when their labor is done, they lie down and sleep, like the brutes. They do not think enough, they should bring their minds into active operation, as well as their bodies.
Men who do much thinking, philosophers for instance, should apply their bodies to more manual labor, in order to make their bodies more healthy and their minds more vigorous and active.
Brigham believed taking care of the mind and body played a large part in the salvation of man:
Until you can govern and control the mind and the body, and bring all into subjection to the law of Christ, you have a work to perform touching yourselves. I delight to talk upon the subject of our organization, but I must do so a little at a time, or I might weary your bodies and distract your thoughts.
Short sermons fitly spoken, are better than long ones ill spoken. May God bless you, Amen. 
John W. Hess, The Juvenile Instructor, XXVII, (May 15, 1892), pp. 302-303.
Brigham was relatively skeptical of “intellectuals”, and his comments might be seen as a directive for some, perhaps even Orson Pratt, to spend a little less time philosophizing.
Interestingly, these remarks are the tail-end of the infamous discourse including the “javelin” blood atonement comments.