Enchiridion by Epictetus, Chapter 13:
If you would improve, be content to be thought foolish and dull with regard to externals. Do not desire to be thought to know anything; and though you should appear to others to be somebody, distrust yourself. For be assured, it is not easy at once to keep your will in harmony with nature and to secure externals; but while you are absorbed in the one, you must of necessity neglect the other.
The Internet Encyclopedia of Philosophy defines "external" in the context of Epictetus's philosophy as:
‘external’; any of those things that fall outside the preserve of one’s prohairesis, including health, wealth, sickness, life, death, pain – what Epictetus calls aprohaireta, which are not in our power, the ‘indifferent‘ things.
Other people's high opinion of you is an external. It's not something within your direct control, and there's a cost to getting it. If you honestly state your ignorance about something, that will lower people's opinion of you. If you work on self-improvement, that can cause people to ridicule you. In general, if you are worried about what other people think of you, you will make progress more slowly.