Employers make mistakes!!! Occasionally it’s intentional, but honest bookkeeping mistakes happen all the time. A lot of it is automated or done remotely by someone you’ll never meet who is responsible for payroll for 100’s or 1000’s of employees. They don’t have the same time or motivation to cross check every line of your pay, but you should!
I put in some overtime and was promised a sizable bonus for doing it over the last 2 years. I usually get a “bonus” anyway for doing night shifts, so every check already said bonus. I did not bother to do the exact math… until yesterday. I found out that 1000’s of dollars had not been paid as promised! I brought this up to my employer, siting all the times when a bonus was offered (keep written records of these conversations/offers), and he found it was not paid out because of a software error in our scheduling system. He immediately apologized and said it will be paid next pay cycle. Even better, he found another time I did not account for and is adding that into the sum I thought I was owed.
Even if you’re an employee and don’t own your business, you still need to manage your business. Make sure you understand everything you are owed, and everything being deducted from your gross pay.