There aren't any rules. You can have a life outside of your startup if you want one. Plenty of people do.
The reasons why people say you can't have one are two-fold. There's a very good, very valid reason, and there's a very bad, toxic-to-your-business reason.
The bad reason is that people who start companies are very competitive. This means they feel they have to be seen doing more, whether it's working longer hours, making more calls, writing more code, going to more networking events, and so on. Sometimes this produces value for their business, but more often it's just "busy work" that isn't actually adding anything useful - going to a networking event and only talking to people you already know is a good example. People who do that sort of thing are the ones who brag about putting in 80 hours a week. Don't emulate those founders.
The good reason to cast your life aside is that very often a startup is doing something ambitious that takes a lot of work to get off the ground, but only has funding to last 6 months. Consequently everything has to be done in that time, which leads to putting in loooooong days. If you have a low burn rate and a long time you can afford to go slowly.
If you take an honest look at the hours people are putting in and realise that half of it could have been done better, or automated away, or just not have been done in the first place, then you'll understand why "number of hours worked" is a pretty awful measure of effort.
Also worth noting that most people haven't read the various studies on productivity against hours worked, and thus just assume - reasonably enough, but usually incorrectly - that over six months, you'll get twice as much work done on 80 hours a week as 40 hours a week.
And working that much feels like you're being very productive.
The reasons why people say you can't have one are two-fold. There's a very good, very valid reason, and there's a very bad, toxic-to-your-business reason.
The bad reason is that people who start companies are very competitive. This means they feel they have to be seen doing more, whether it's working longer hours, making more calls, writing more code, going to more networking events, and so on. Sometimes this produces value for their business, but more often it's just "busy work" that isn't actually adding anything useful - going to a networking event and only talking to people you already know is a good example. People who do that sort of thing are the ones who brag about putting in 80 hours a week. Don't emulate those founders.
The good reason to cast your life aside is that very often a startup is doing something ambitious that takes a lot of work to get off the ground, but only has funding to last 6 months. Consequently everything has to be done in that time, which leads to putting in loooooong days. If you have a low burn rate and a long time you can afford to go slowly.
If you take an honest look at the hours people are putting in and realise that half of it could have been done better, or automated away, or just not have been done in the first place, then you'll understand why "number of hours worked" is a pretty awful measure of effort.