That is Amara's Law [1]. The paraphrase given by Cringely that is commonly quoted (to my knowledge, Amara himself never gave as concise a quote as the paraphrase) is:
"We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run."
"We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run."
[1] https://en.wikipedia.org/wiki/Roy_Amara