As a former solo founder, "just toughen up" is very bad advice. It's not something to just power through, and trying is likely to be bad for your mental health.

As a former solo founder, "just toughen up" is very bad advice. It's not something to just power through, and trying is likely to be bad for your mental health. Much better advice would be to get a cofounder and/or join a startup program or some other group of peers.