Are there any common things in adulthood that seem simple but are actually really difficult?

For me, accepting rejection is one of those things. It's something we all face at some point, whether it's in relationships, jobs, or even just in daily interactions. You’d think it’s a simple part of life, but it’s surprisingly hard for many people to handle. When someone says “no,” it’s not about personal failure; it’s just that things don’t align. But still, so many people react defensively, or worse, try to guilt-trip others into changing their minds.

What about you? Are there any common things in adulthood that seem simple but are actually really difficult? Maybe things like budgeting, managing time, or even just learning how to set boundaries without feeling guilty?