Greatness as Jesus measures it is a useful diagnostic, because it is so easy to test.
Take the last week and ask a blunt question. Who was I serving, and who was serving me? Not in principle, but in actual hours and attention. Then look at the tasks you volunteered for and the ones you found a reason to avoid.
A pattern usually appears. Most of us are glad to serve when the service is visible, strategic, or likely to be noticed by someone whose opinion matters. The test is not whether you serve. It is whether the absence of an audience changes how much you are willing to do.
So try something today. Do one useful thing for someone who will never know it was you, and then refuse to tell them.