The difference between an amature and professional plumber
An amature plumber makes multiple trips to Home Depot to buy supplies, a professional plumber gets supply from his/her truck.
An amature plumber listens to whatever advise other people gives, a professional plumber does not need them.
An amature plumber buys much more stuff than what's needed, a professional plumber knows exactly what's needed.
An amature plumber does not know he/her is supposed to customize pieces to fit everything together, a professional plumber knows what standard piece to use and what needs to be customized.
An amature plumber does not know what is too loose, what is too tight, what does the building code say; a professional plumber has been trained to know those things.
An amature plumber uses his/her spare time and charges nothing, a professional plumber does plumbering for living and may charge $200 a hour.
An amature plumber will be very happy after a sink, faucet, or a food processor is installed; a professional plumber needs to look for another project.
Between amature software engineer and professional software engineer, where am I?