The brain is the organ that learns, so it is designed to be changed by your experiences. Amazing! Whatever we repeatedly sense & feel & want & think is slowly but surely sculpting our neural structure. Prolonged, repeated mental/neural activity - especially if it's conscious - will leave an enduring imprint in neural structure, like a surging current reshaping a riverbed.
The brain takes its shape from what the mind rests upon. If you keep resting your mind on self-criticism, worries, hurts, comparisons, then your brain will be shaped into anxiety, depression, anger, sadness. On the other hand, if you keep resting your mind on good events and conditions, pleasant feelings, natural pleasures, positive things, moments & people in your life, then over time your brain will take a different shape - one with optimism, a positive mood, a sense of worth, strength & resilience.
What you choose to pay attention to - what you rest your mind on - is the primary shaper of your brain. And, on the whole, you have a lot of influence over where your mind rests.