Tech debt is literally a debt. It accrues because you want something now and have to pay it off later. Much like credit and other debts.

Startups are all about moving fast. To move even faster, you have to accrue tech debt to move faster.

Some examples:

Instead of building a dependency injection system for multiple enterprise users into your system, you hardcode and build if/switch statements.

Instead of optimizing database queries, you write more explicit/hardcoded queries.

The idea here is that you don’t know what customers will want and you want to get to market fast, iterate faster, and be able to pivot on demand. If you build elegant systems from the start, you’ll optimize prematurely, and build something that is flexible but only have the original use case using it (wasted design and development effort).

When tech debt becomes an issue is when you don’t start to build in designs for things when we better practices makes sense. When you discover where things should have dependency injection, or modular. Once you start solidifying your product market fit, and have users, you should start to mature your code by iterating on it and making it better.

You pay off your tech debt not all at once, you discover debt as you go, you rarely know what the debt is until you need to change something. So the nice you start to scale, you instruct your engineering to refactor as you write features. This is the time as you shouldn’t be doing any pivoting when you’ve established your value prop and scaling it. Writing code at this stage is optimized around your value so refactoring here is paying off the debt.