I have been an entrepreneur for almost 10 years now. The last 3 years a startup founder and I can say that it is a totally different world. I have felt the pains and gains related to founding team relations to building the product; from finding your ideal customer profile to validate the market; from finding your first customer to finding the best channels to grow your customer base.
Having those ups and downs has made me an advocate of having some activities besides your startup that balances you - is it sport, is it knitting, it doesn't matter, but it has to matter to you.