sidelines of

The idea behind Wetpaint came to us when one of our friends was diagnosed with cancer. After the initial shock wore off, he did what most of us would do; he went online to learn everything he could about the disease. He found lots of facts, but not the stuff he really wanted to know—like how other people with cancer were coping. As we sat helplessly on the sidelines of our friend's dilemma, it dawned on us: why not make it easy for groups of people to share information, experiences and build social communities around anything they want?

Please explain to me what "sidelines" means in this context?