A partner can help provide necessary resources to help the business.

Your ideas, as they rattle around in your brain, get bigger and bigger until you may feel that they are absolute fact. 

in small firms you have the founding architects doing very little architecting, founding accountants doing very little accounting, founding lawyers doing very little lawyering

When you start the business, you dream of the freedom to practice your particular talent your way, with no red-tape, no bureaucracy, no restraint.