The yes arrived before you did.
The request sounds reasonable. You say yes. Then you realize you have promised the same hour to three different people, including yourself. The rest of the afternoon becomes an argument with a decision you already made.
Before the next optional request, try making room for an actual answer.
Capacity is information.
Look at the calendar. Consider the commitments you have already made. Being clear about what you can do is more useful than making a promise you are hoping a future version of you will somehow keep.
A boundary does not need to be a statement about the other person’s character. It can simply be an honest description of your availability.
Say the useful part.
“I cannot take that on this week.” “I can help for an hour, but I cannot lead it.” “I need to check my schedule before committing.” These sentences leave less room for misunderstanding than a reluctant yes with an invisible list of conditions.
Use language that fits your relationship and obligations. Some commitments need a conversation rather than a quick refusal.
Protect the yes you mean.
The goal is not to become unavailable to everyone. It is to make your commitments more deliberate. One clear limit today can make room for the responsibility you genuinely need to show up for.
I can help with this part, but I cannot take on the whole thing.