It's ok to be frustrated.
(This a frustrated Eames face.... usually I'm not snapping pictures when he's hopping mad, so this is just "mildly annoyed.")
Some mothers go to great lengths to make sure their babies never experiences frustration. I, myself, have made a personal policy (yes, even at this young age) of allowing frustration to work itself out with my son.
I don't jump up to solve his problems. I let him find a solution that can he can settle with. My hope is that if my baby can learn by experience that problems take time, patience, and thought to achieve resolution, then he will carry this ever-present truth into the rest of his life.
When he is yelling at a toy that won't go in his mouth, I will tell him with a gentle smile and compassionate eyes, "It's ok to be frustrated. You can do it. I love you."
I know he doesn't understand these words. I know we're not actually having a direct teachable moment... but he does respond to my demeanor & my facial expressions. He receives assurance that nothing is actually WRONG in this situation. Nothing is BAD that he needs to be saved from. Mommy doesn't need to swoop in and FIX it. Plus, I am practicing responding to screeches and screams with calm equanimity and confidence-building-patience of my own.... so when he's 4 years old and we experience the same thing, hopefully I'll respond the same way.
We applied this theory to helping him learn to sleep also. It's been very successful.
The key here is "Helping Him Learn." Life is full of lessons. We don't need to teach them all. We DO need to let the learnings sink in. So... it's ok to be frustrated.