Harj, a Y Combinator partner, introduces the considerations for working at startups and discusses Paul Buccheit's perspective on choosing between startups and stable companies.

• Understand that working at a startup is unique and not for everyone; it often means less pay and more work.
• Consider personal contentment and desire for change before deciding to work at a startup.
• Paul Buccheit advises against moving to a startup if the trade-offs of lower pay and longer hours are unappealing.

Harj explains how to assess a startup's potential success by considering its growth trajectory, user engagement, and the depth of passion users have for the product.

• Look for signs that the startup is already on a path to success, such as increasing user numbers and revenue growth.
• Focus on the growth trajectory rather than the absolute numbers to gauge potential success.
• Identify startups where users are deeply passionate about the product, even if it's a small group.

The importance of being impressed by the startup's founders and team is emphasized, valuing their achievements over traditional credentials.

• Evaluate the founders and the team they have built; be impressed by their achievements and potential.
• Look for founders with unconventional backgrounds who have demonstrated exceptional achievement compared to peers.
• Evaluate founders based on their relative success and the unique traits that make them likely to build an extraordinary company.

Harj advises against evaluating the size of the market a startup is in and instead suggests looking for a passionate core user base as a sign of a promising startup.

• Avoid trying to evaluate the size of the market the startup is in; many investors miss out on great opportunities with this approach.
• Seek startups with a core group of early users who are fanatical about the product, like Airbnb had in its early days.
• Talking to users and gauging their love for the product can be a strong indicator of a startup's potential.