Solo founder here. Same advice with the caveat that 98% of people should never be solo founders - you must be able to code and sell - but even if you can you should still get a partner if they double your speed.
The few solo founders I have personally dealt with have fit that description exactly.
Reality is no one is so good that having another voice in the room isn’t usually an advantage for the leaf nodes. There are plenty of people who believe they are, though.
I will say this only applies to more traditional startups - seeking funding, hiring a team. It’s different when the solo entrepreneur builds and sells and then is hiring to augment the company. Not sure I would join that either but it is different.
Pros and cons to both paths.
I think the biggest reason not to go solo, is not many people are good at both the tech AND talking to customers and thinking big picture.