A portrait is a painter and the model. Any third person will look at it and think, “Damn. That’s a fine figure painting!” Meanwhile the model thinks, “Do I look like THAT?!” Her friends reassure her that the artist is a jerk. The model’s husband thinks, “There’s something wrong with the mouth.” (John Singer Sargent rolling in his grave), and the painter thinks, “Why did I even start this?”

Everyone else, EVERYONE, thinks, “WOW! That’s damned fine. I wish I could paint like that.”
This is true for most artist/painters and their work.

So, just start. Get in there and start thrashing about and you’ll do fine. And if it’s not so fine you train yourself to have a short memory like the pitcher in baseball. Guy hit a home run off your last pitch? Forget it, you’ve got to pitch the rest of the inning.