Discovery.

Reynolds, Self-portrait when Young, 1758

By leaving a student to himself he may be led to undertake matters above his strength, but the trial will at least have this advantage: it will discover to himself his own deficiencies and this discovery alone is a very considerable acquisition. 

Our studies will be forever, in a very great degree, under the direction of chance; like travelers, we must take what we can get, and when we can get it – whether it is or is not administered to us in the most commodious manner, in the most proper place, or at the exact minute when we would wish to have it.

Sir Joshua Reynolds