TWO drug addicts so desperate to finance their addiction they took part in taxi robberies ''doomed to failure'', were yesterday sentenced to five years in jail. Kwong Kwok-kuen, 34, and So Yuet-leung, 32, pleaded guilty to three counts of robbery in April involving a total of $1,890. So also pleaded guilty to a further count of possession of an offensive weapon. The District Court heard three taxi drivers were threatened at knife-point and tied up with shoelaces in Aberdeen. Defence counsel Luke McGuinniety told the court the defendants had extremely difficult backgrounds. So's father had been executed for smuggling and he had been brought up by a sister who was married for a dowry when she was 15. He was then left to fend for himself. Kwong had a ''horrific'' leg injury which prevented him from continuing as a construction site worker. Mr McGuinniety described the robberies as ''thoughtless, stupid, illogical'' and ''doomed to failure''. He said the pair committed the robberies within the space of a few days in virtually the same place, and on each occasion took enough money to finance a day's drug-taking - in short ''three robberies, three fixes''. In sentencing, Judge Hawkes told the court: ''These offences can only be regarded as being serious.'' He said he was taking into account their guilty pleas and their backgrounds, which could be considered to be reasons but not excuses. He sentenced So and Kwong to five years on each of the charges of robbery to run concurrently. In addition, he sentenced So to six months for possession of an offensive weapon, again to run concurrently.