You're not given a short life — you make it short

Seneca opens by rejecting the common complaint that nature is stingy with our years. The real problem is squander: we spend enormous stretches of time on things that leave nothing behind — idle luxury, other people's quarrels, ambitions that were never ours to begin with. A life can run seventy years and still amount to almost no living, because presence, not duration, is what counts.

He compares it to a large estate in careless hands versus a small one well managed: size isn't the deciding factor, stewardship is. Most people discover this only near the end, when they finally look back and realize the years technically happened to them without actually being used.

The practical sting is that this isn't a future problem to solve later — the squandering is happening in whatever way you're spending today. You don't need more time; you need to stop leaking the time you have.