I don't think you ever really need to punish yourself for any decision you make. If it's a mistake, the consequences will teach you to choose differently next time, rather than shame. You don't need to be hard on yourself at all. Life is hard enough. And I don't think you need to worry that without shame you wouldn't be motivated. Shame is actually the least effective motivator, let alone incredibly damaging to your mental health. It's not mandatory to feel shame for things. I know it was taught to you, and hard to unlearn, but you are allowed to let go of being hard on yourself.