As previous post...or find unis that have excellent extra-curricular drama groups/comedy troupes that you can get involved in.
Acting is a risky proposition, no doubt, but the lottery analogy is flawed, since there's virtually nothing you can do to improve your chances of winning the lottery, it is purely luck. Luck is undoubtedly a significant factor in acting, but there are things you can do to increase the chances of luck working in your favour. Let's say in five years' time, you and a random person off the street audition for a part. Who's got more chance of getting it: you, the dedicated, RADA-trained, and determined actor (or actress, if you prefer) or the completely unprepared acting newbie? Admittedly, in reality, it's never that straightforward, and there will often be other RADA-trained actors who get the part instead of you, but my point is, unlike lottery results, you can do things to influence your destiny in auditions.
I don't think you should look at it at this stage as "will I succeed or not?" I think you need to be looking at it now as "am I prepared to tough it out and work really hard at this, often for far less reward than students of other subjects will get for less work?" If the answer to that is yes, crack on and do it. If the answer is no, you're better off listening to the naysayers and following an easier path in life.