It is easy to be convinced to take someone on as a business partner by their reputation or talk. Yet, just because someone has succeeded elsewhere does not mean they will do so again. It also does not mean you will be better off having them onboard.
Sometimes it is better to keep a company smaller, do things your way and grow organically. Be sure the other person has something that will make a difference, something you could not acquire yourself.
What are you willing to sacrifice for their help?
Remember how you took the entire week off work to look after your child? Or how you gave your employees a bonus to celebrate a good month? When you enter into a partnership, you might miss that freedom to do as you please. You will no longer be entirely your own boss and will have to share decisions with your partner. You will also have to split the profits.
What happens if the company requires more capital?
If a potential partner has more wealth than you, this is something to watch. If you do not carefully word your contract, it could reach a point where they can take control by insisting on an investment you cannot match.
How can you separate?
Hoping things will work out is fine. Assuming they will is naive. A huge percentage of business partnerships fail, be that quickly or after years of working together. If you ever need to separate, it will be more straightforward if you have guidance on how to do so in your partnership agreement. Things to think about include: How do you set the price, does the other partner get the first refusal and can they veto potential buyers?
Understanding more about the legalities of business partnerships will be crucial to ensure you do not make a decision you regret.