The opponent-process theory was developed by Richard Solomon during the 1980s and it claims that an increase in positive feelings will be followed by an increase in negative feelings a short time later. Similarly, an increase in negative feelings will be followed by a period of positive feelings. The opponent-process theory also claims that this mechanism is strengthened with use and weakened with disuse so people who are substance users will after some time need more of the substance to achieve the same results, in other words, they develop a tolerance to it. At the same time, the negative feelings that follow substance abuse tend to intensify. Of course for people who take the substance, the intense pain will only be alleviated by more of the substance. People will often continue use of the substance as a way of avoiding withdrawal symptoms. This is why many people become extremely addicted to the substance and cannot function without it, making this a very dangerous cycle in which people can very easily overdose trying to reach the euphoric high that they once felt with a much smaller quantity. A study done by Solomon on skydivers examined the emotions involved in first-time and more experienced jumpers. The first time jumpers experienced extreme fear before jumping which was then replaced by relief when they land. The experienced skydivers, on the other hand, experienced great euphoria when the jumped and it lessened when they landed. After a couple more jumps from the beginners, they too started to experience euphoria as they jumped as opposed to fear. This study has often been used to link drug abuse to this theory. Users will use a certain amount of the substance until it no longer gives them the same results and then increase dosage to avoid withdrawal symptoms. This theory is an attempt at understanding the connection between emotional states and motivation, and because it is relatively new there is not much research that supports its usefulness.