By successfully limiting Iran's ability to trade, their economic growth has been limited. This leads to fewer options for accessing material required to create weapons grade nuclear material. Beyond that, sanctions have also included very specific items and materials required to perform the action directly. Iran is still making small advances towards a nuclear weapon, but sanctions have significantly slowed that effort.
I'm not usually one for sanctions, but in the case of Iran, they have been crippling enough to stop their nuclear program from developing. And this is even with warnings given by the Chinese and the Russians. And I am pleased to see they have worked. Would never want to see a nation like that armed with nukes.
Sanctions have affected Iran's overall economy and kept them from developing a nuclear program to the point of having weapon at the current time. However, the program has continued to develop as Iran believes it will result in greater regional power overall and ending its lack of ability to negotiate internationally. Only a strike or regime change can stop Iran from becoming a nuclear power.
Iran had sanctions against it for years and years and went forward with their nuclear program, at the cost to their citizens which the governing body does not care about. Only recently have talks gotten the program to stall, and that's probably only temporary. Iran doesn't care about sanctions because they don't impact the top 1% in Iran.
Iran is a arch enemy of Israel. They will develop nukes to intimidate and perhaps to even decimate Israel. They would not stop building nukes unless they are invaded and taken over by another country. The goal is to build nukes to become a force to be reckoned with and they will not deviate from the plan.