If everything goes well you can buy a lovely house in the suburbs, raise 2.5 kids, grow old together with your wife and live happily ever after.
If it goes wrong she takes your kids and half your assets immediately, followed by several years of child support and possibly alimony.
It's not like you have a coin flip chance at a happy life or an unhappy divorce. You can influence the odds here. In fact, you can really stack the deck in your favor, so to speak.
Sure, people lie and people change, but it's not like you have to get married after a certain amount of time. You can wait to see what the person is like at their worst and then decide. Yeah, it's a 2 way street and you have to work with their timetable too. But no one is forcing you to just jump into a marriage blindly.