Motivation is [IMHO] the biggest single challenge we face in the realm of fitness. . .not just cycling. Think about it. It's uncomfortable. It's cold. It's hot. It's wet. It's sweaty. It's a pain getting all the gear set up for a ride. There's family, work, and a billion other priorities. There are lots of mundane forces working against you!

Here's a view:

Integrate fitness into who you are rather than what you do. Look to the community of cyclists (like this forum) for support. Carve out fitness as one of those inviolate things you do for YOU. Seek out others in your private life that share the view. Take personal pride in these choices and inform those around you that such things are central to your happines. . .and that support on the part of friends and family will be reciprocated in the form of support for their goals. . .and follow up with action.