Why is it important to be reliable in the workplace?

Because if you’re reliable and trustworthy, your employer will know that he/she can trust you to get things done, and he/she won't hover over you so much, breathing down your neck about a project that's due or whatever. They'll leave you alone a lot more, and you won't have as much on-the-job stress. Also, you'll look like a really massive asset to the corporation, and when it comes time for your annual performance review, they'll give you a good raise to make sure you stay in the company, because they want to keep their most valuable employees.