I just did the math on this, your chances of missing are ~50% at 10 RANDOM relays each. Adding 10 more decreases it by another 50% to 25%, etc. This math ignores the fact that in practice many common, large relays bring this number down massively.
Discussion
It also ignores the fact that as a general rule, the people who you are wanting to communicate with are likely going to be gravitating to the similar virtual space and relays as you.