Having fallen behind to Harry Kane's early goal, Leicester forced their way back into Friday's match at the King Power Stadium through Leonardo Ulloa.
However, a lapse in concentration from Ben Hamer allowed a Christian Eriksen free-kick to sneak in at the near post and secure a 2-1 win for Tottenham.
Pearson – who spent the match in the stands serving a one-game touchline ban for abusing a fan – felt his side had been much the stronger and rued more bad luck.
"I don't know where the black cat is and whether we have run it over but it is a particularly disappointing outcome because our performance was very good," he told BBC Sport.
"We caused them a lot of problems but are falling short of seeing games through.
"That remains a big frustration and we need to change it very quickly. We have to continue to strive towards working as hard as we can to change that. The bottom line is at this level the quality is the defining factor.
"A lot of our play has been exceptionally good but we have not made the most of our own chances. The winning goal comes out of nothing and Ben Hamer would expect to save it."
The defeat means Leicester's winless run now stands at 13 league matches, and they sit six points adrift of safety.
