Has Twitter lost its wings?

Twitter has been struggling for some time now to adequately define itself in the social media sphere and set itself up as a real contender for market share. There doesn't appear to be a concerted marketing strategy which has led to a stagnation in user numbers and confusion over its usage, which means that Twitter is struggling to clearly define its market share. Can it compete with successful rivals such as Facebook and Snapchat, or as The Economist argues, has it let its chance fly by?