Captain’s log, stardate 20210413
When a prospective client requests that you agree to a deadline for a proposed project, ask them this:
What are the consequences of missing the deadline?
If there ARE serious consequences, then you should respect the deadline, and increase your fee accordingly to accept the increased risk.
If on the other hand, there are NOT serious consequences to missing the deadline, you should point it out as an arbitrary constraint and politely insist that they drop it if they want to work with you.