There are many ways to know when you've been successful. One of the best ways is to set goals using SMART goal system. Goals should be specific, measurable, attainable, realistic and time based. If you wrote goals on a piece of paper and you've met those goals then you've probably reached them. There are many ways to keep track of your goals and how you keep track is really dependent on what works for you. For short and long term goals a journal is helpful so that you can see progress and changes particularly over time. Writing short term goals on a calendar is helpful. A calendar is based in time and it will give you a good time perspective of how you are progressing from day to day. Daily goals can also be written on sticky notes and put up in areas where they can frequently be seen as a reminder.
At some point fitness goals aren't about reaching goals written on a sheet of paper. It's about feeling better, looking better and being healthy. Can I climb more stairs than I did before? Can I walk further than I did before? Am I out of breath less often? Did I make it to the gym?