Obstacles can be anything or anyone that gets in the way of you reaching your goal. Realizing that there will likely be obstacles along the path to your goal makes it easier to plan for, overcome or avoid them.
Obstacles can come in two forms: roadblocks and real limitations. A roadblock is an obstacle which you have the power to control. Many roadblocks are very real and cannot be changed or removed - these are called limitations.
All opportunities lie in areas which you CAN change. It is important for you to decide whether the roadblock is a true limitation, something that you are unable to change, or not. Accepting any limitations requires you to be really honest with yourself and you may need to adjust your goal accordingly. Don't waste energy on things you can't change at the time.