In mathematics, probability is defined as a chance that something will happen. For example if you toss a coin , the probability of heads or tails turning up is 50% or half . Now let us put constraint like toss of two coins. The chances of both turning tails is .5 * .5 which is equal to .25. As you keep adding constraints, the probability of something happening in a sequence goes down.
In entrepreneurship and for startups , the chance of being successful is very less. The constraints are too many. Either there is a lack of funding or a good team or untested product. The entrepreneur walks the really tight rope to success. One misstep and whole project may be ruined resulting in loss of money, time and career. It is also factually true that many startups do not gain the traction they need to.
That is how world looks at entrepreneurship ( low probability of success).
A true entrepreneur however never looks at the probabilities because they are discouraging enough. She looks at the possibilities. She looks at creating product and services that are difficult to say no to. She looks at creating systematic value addition to her work. She looks at building relationships and skills.
The thought of being scared by low probabilities is akin to making excuses. Thinking about what will not work is not going to help. Losses cause more more pain than the equal amount of gains. So it is not the right strategy to think only of losses all the time. One may fail if one tries to do something but there are no chances at success if one never tries.
Probabilities of success are low when you take a risk though still better than no probability at all.