For the chronically over-yes.
Every yes is a quiet no
Every yes to the wrong thing is a no to the right thing
The Stoic Principle
The opportunity that 'looks good on paper' is asking you to fund it with the only currency you cannot replace. Time. Saying no is not a rejection. It is a budget.
The Stoic Support
"If you seek tranquility, do what is essential. Do fewer things, better."
Marcus Aurelius | Meditations
Stoic Steps for Radical Resilience
Five steps for protecting the work you already said yes to.
Name what this 'yes' costs you
Hours, evenings, mental bandwidth, the project you are already on. Most yeses get said before the receipt is even printed. Print the receipt first.
Ask: would I take this if I had it already?
If you would not accept this as a current obligation, do not accept it as a future one. The future is going to be just as full as the present. (Probably more so.)
Run the two-year test
Will this matter in two years? If yes, it might be worth the price. If no, you are optimizing for someone else's pat on the back.
Decline with kindness, not justification
'I cannot take this on right now' is a complete sentence. Long explanations are negotiation invitations. Short and warm beats long and apologetic. Every time.
Say yes to the no
The 'no' protects the 'yes' you already made to the work that matters. Picture the yes you are protecting before you decide. Then decide.