For motoring journalist Tim Barnes-Clay it was being involved in a crash and having children.
I'm an ex-motorcyclist. Being involved in a serious crash and then becoming a father was why I stopped being a biker.
But I do miss life on two wheels. For one thing, it was always quicker getting to work, plus motorbikes are generally cheaper to buy and run than cars.
However, motorcyclists are 75 times more likely to be killed or seriously injured than car drivers, according to the Department for Transport (DfT).
Increase in motorcyclist casualties
Figures from the DfT show there were 362 motorcyclists killed in the UK in 2011.
Now, this is a 10 per cent fall compared with 2010, which is good news. However, the number of motorcyclists seriously injured rose by 10 per cent to 5,247 in the same time period.
What's more, the total reported motorcyclist casualties went up by 8 per cent to 20,150 in 2011.
Naturally, the DfT says it wants to see a reduction in the number of bikers killed and injured.
Drivers urged to 'think biker'
"Motorcycle safety is a priority issue for the government's THINK! [road safety] campaign," says DfT spokesman Simon Larson.
"We recently ran a THINK! BIKER initiative campaign encouraging drivers to take longer to look for motorcyclists.
"We also launched Stay in Control, a partnership scheme promoting defensive riding messages to motorcyclists."
Chris Hodder of the British Motorcyclists Federation (BMF) says more people per mile get injured on motorbikes than in cars.
However, he says much of the peril comes from other road users.
"Studies such as the Motorcycle Accident In Depth Study show that two-thirds of accidents are caused by car drivers.
"But there is a lot riders can do reduce their own risk such as taking advanced training, riding defensively and investing in protective equipment," he says.
Being a biker & driver can cut insurance costs
Indeed, many bikers also have a car, and the BMF claims that riding a motorcycle makes you a better car driver, with many insurers giving reduced premiums to these dual drivers.
Gemma Stanbury is head of car insurance at Confused.com.
She says: "Insurance providers weigh up your risk of making a claim, and set premiums – the cost of your cover – accordingly.
"Some insurers take the view that by driving two vehicles, you are a more proficient driver and may reward you for this with cheaper premiums.
"Also, because you drive both a bike and a car your use of each is reduced and so, ultimately, is the risk to your car insurer and your motorbike insurance provider of you making a claim.
"Because of this reduced risk that both insurers face when covering you, again, you may be rewarded with cheaper premiums."
Are motorbikes worth the gamble?
But Clare Morrison of road safety charity Brake doesn't think motorbikes are worth the gamble.
"Motorcyclists continue to make up a huge proportion of casualties on our roads, despite only accounting for a small proportion of traffic.
"This is partly down to them being vulnerable, as if they're in a crash they're exposed to the full force of the impact because they have no vehicle around them.
"Also drivers often fail to spot motorcyclists, and some bikers put themselves in danger by riding too fast," she adds.
"Clearly, it's critical that people who choose to ride do everything they can to preserve themselves: wearing protective gear, staying well within limits and avoiding overtaking.
"We also urge drivers to help guard people on bikes, especially by carefully checking mirrors when changing lanes and looking twice and 'thinking bike' at junctions," concludes Morrison.
'Common misconception' that bikers crash more than drivers
Conversely, road safety charity the Institute of Advanced Motorists (IAM) says it's a common misconception that motorcyclists are more likely to be involved in a crash than car occupants.
In fact both parties are equally likely to befall this fate, says IAM spokeswoman Caroline Rheubottom.
But, regrettably, it's simply that those on motorbikes are the ones who're likely to come off worse, Rheubottom says.
"Riders aren't being sheltered by the metal bubble or integrated safety systems which car drivers often take for granted.
"Motorcycling can be a great way to get around and can be hugely enjoyable.
"But the key to bringing down the worrying motorcyclist killed and seriously injured figures is education and training."
Weighing up the risk
So, even though the statistics speak for themselves, it's up to us as adults to weigh up the risks we choose to take in life.
I may have hung up my leathers during my child-rearing years, but for some reason I've not thrown my biker kit away.
There's just something about two wheels that grips your soul, and doesn't ever quite let go.