The short answer
You've built a life where work always has permission to cut the line. Friends don't send urgent Slack messages, so they lose by default. The fix isn't better scheduling — it's deciding, once, that a promise to a person counts as much as a deadline from a boss.
You've built a system without meaning to. Work is loud, urgent, and right in front of you. Friends are patient — they'll understand, they'll reschedule, they'll quietly stop asking. So work wins every single time, not because it matters more, but because it asks louder. Research on self-regulation and procrastination shows this clearly: when we don't set firm rules ahead of time, we default to whatever feels most pressing in the moment. Friendship rarely feels pressing until it's gone.
Marcus Aurelius put it plainly: you either stay in the life you have and accept it, or you choose to change it. There is no middle ground where you keep canceling and also keep the friendships. The life you've 'been used unto' — always available to work, always optional to friends — is a choice. You're just not making it consciously yet.
This week, pick one standing plan and treat it like a flight. Tell your work contacts the night before: 'I'm unavailable from 7 to 10 p.m. Thursday.' No apology, no over-explanation. Then show up. One kept plan won't fix everything, but it will prove to you — not just to your friends — that the line can actually hold.