A more thorough explanation:

The wait-and-see principle is a legal concept that modifies the rule against perpetuities. It allows a court to determine the validity of a future interest based on whether it actually vests within a certain time period, rather than on whether it could have vested outside that period.

For example, let's say that a wealthy individual creates a trust that will provide for their descendants for generations to come. The trust includes a contingent future interest that will only vest if a certain event occurs more than 100 years from now. Under the traditional rule against perpetuities, this interest would be considered invalid because it could potentially vest outside the allowed time period. However, under the wait-and-see principle, the court would wait and see if the interest actually vests within the time period before determining its validity.

The wait-and-see principle is also known as the second-look doctrine.