Your word is a currency. Break it enough times and nobody accepts it anymore.

What you say you will do is accepted on credit, and like any credit it depends entirely on a record. Each kept commitment is invisible and each broken one is not, so the balance moves down faster than up. Once it runs out, people stop making plans that depend on you, usually without ever telling you why.

Promise less than you could and deliver what you promised. If something will not happen, say so before the deadline, since an early no protects the balance and a late silence spends it.