If thou wouldst make progress, be content to seem foolish and void of understanding with respect to outward things. Care not to be thought to know anything. If anyone should make account of thee, distrust thyself.
The Golden Sayings of Epictetus, CLVIII, Page 174
If thou wouldst make progress
Are you perfect in every way? Do you care to better yourself? If not, this passage is not directed at you. The first step in growing is desiring growth.
be content to seem foolish and void of understanding
Here, Epictetus is encouraging the listener to do two things. First, discard your pride and be content to pursue goodness in spite of your seemingly foolish actions. Second, realize that every new endeavor requires an ignorant phase. Do not miss out on what you could just so that you can maintain a reputation of intelligence.
with respect to outward things
The most important aspect of the first sentence. Do not place a high priority on externals. This is the heart of Epictetian philosophy. When you allow an external factor to determine your peace of mind, you no longer get to decide your emotions. It is giving your freedom away to be ruled by something that could change no matter your best efforts. Instead, pursue virtue. This is what he means by progress.
Care not to be thought to know anything.
A more blatant charge to ignore your reputation. Pride will lead you down a dark and unfulfilling path.
If anyone should make account of thee, distrust thyself.
This might be the most influential aspect of this excerpt for me. We are much more prone to distrust the critiques of others. But praise is rarely examined. But here Epictetus suggests the distrust of praise. When you are praised, examine it. Determine whether or not it is actually truth.