Most terrorist organizations are always unsuccessful in their goals, there's only been about 7 percent success rate and most of these organizations result to violence. However, instances of success has been recorded by well-known terrorist forces.
Some examples include: Hezbollah, which succeeded in two of its goals: driving peacekeeping and Israeli forces out of southern Lebanon in 1984 and in 2000. The Tamil Tigers also won a major victory, taking control over parts of Sri Lanka starting in 1990.
The disadvantages of terrorism generally outweigh the advantages. Terror is a cheap way to inflict pain on the other side. Terrorism is useless for taking or holding territory. Non-terrorist movements are far more likely to win a settlement or an outright victory. Terrorist movements tend to lose.
Terrorism prolongs wars, and terrorist groups often lack clear political goals. The majority of terrorist groups end their violence without securing their central strategic aims. Although they most certainly achieved their short-term objectives of generating attention, fear, and publicity. For the most part, terrorists do not gain any of their long-term goals.