squeak-
Sorry if I worded it wrong.
In most cases you will not get a prime number when multiplying a few primes and adding 1. If the number 2 is not one of the primes then there is no chance of (product of the primes) + 1 being a prime since it will be an even number and divisible by 2.
The exception to the above rule is when one of the primes is the number 2. In that case the (product of the primes) + 1 will be odd and the probability of it being prime is greater than 0% (but less than 100%).