In context, Galatians 6:4-5 is actually about pride. It's not about not underestimating your skills, but rather about overestimating your value. However, I am of the opinion that self doubt is almost, if not just as bad as pride, and so should be eliminated by the same token.
In the header image, I present a screenshot from a conversation I once had with a friend. She's an extremely talented artist, capable of drawing some adorable creatures, and I was very privileged in that once, she drew a picture of me and my dog. But she always doubted her skills. She would reason that some people are better at drawing than she is, and so therefore, she must be nothing.
I truly believe the Lord gave me the response I gave her. I grabbed two of my butterfly photos and asked which is prettier. She preferred the lacewing over the comma, but agreed that the comma is still very beautiful. This seems to have worked. Although she still feels strange accepting compliments, she seems more confident in her skills. Rather than comparing herself to others, she now stands by her own steam.
When the Lord judges us, it will be as if there was no other significant being in the universe. What you do with what God gives you is between you and God, and so this should be our focus. Never mind what someone else has or what they do. Focus on yourself and the Lord, and you will have neither pride nor self doubt. You will be perfectly at peace.