For me there was no "click"... just a series of events.
I'm in the military. A number of years back I returned from overseas in a bit of a shit state. After living in a constant state of high stress for an extended period of time a sudden lack of stress tends to make one feel... off. In my case it was apathy. I just found it hard to care or put effort into anything. I used to play a lot of sports but never got back into any of them after returning home, and as a consequence my physical fitness tanked.
After awhile I started suffering from minor injuries while doing minor physical training. I think it was due to muscle imbalances, or maybe it was because I thought I could push my body harder than I actually could and I'd push it past it's (now much lower) limits.
I tried several times to get back into shape by running, but each time I'd injure myself and each injury would set me back even further.
Then one day I was researching conditioning methods when I looked down at my thighs. I used to have a massive set of wheels and over the years they've atrophied to the point where they looked like skinny old man thighs. I decided to get back into sports and use athletic training methods to get me there, and in the process I discovered the world of strength training.
8 weeks of Starting Strength re-inflated muscle I thought that I'd lost and I then switched to 5/3/1 to lower the intensity and make room for athletic conditioning.... which is where I sit today. 3 cycles of 5/3/1 complete and still working on building myself back up. It seems that despite the great gains I've made in gross strength I'm still lacking a lot on both the endurance and stability fronts.
One of the reasons I like Jim Wendler is that he's a former athlete that lost his way, only to regain it later in life. He says that for every year you let your conditioning drop you should expect to spend a year rebuilding. At this rate I have about 4.5 years of rebuilding to do, but I'd rather do that then walk around as some gibbled old man. I'm moving in July which writes off the summer sports season but I plan on joining some sort of sports team this fall. The city I'm moving to will be much bigger, so they'll have much more to offer.