What is the meaning of [Blessed is he who expects nothing, for he shall never be disappointed]

Don’t be too optimistic about the future. Remember that There’s many a slip
‘twixt the cup and the lip

Alexander Pope, who wrote this on October 6th, 1727, in a letter to John Gay,
described it as ‘a ninth beatitude added to the eighth in the scripture’. The
reference is to Matthew, v, 3-10.