a constant source of annoyance or trouble
una fuente constante de molestia o problema (una fuente constante de molestia o problema)
"The trade dispute has become a thorn in our side."
"La disputa comercial se ha convertido en una espina en nuestro costado." (La disputa comercial se ha convertido en **una espina en nuestro costado**.)
to trust someone even though you may not have all the facts
to start working hard, especially after delaying
to keep working steadily on something
a small visible part of a much larger problem
you can’t achieve anything if you don’t take risks
to cause extreme fear or horror