Adde parvum parvo magnus acervus erit.
(Add little to little and there will be a big pile)
Publius Ovidius Naso (app. 9 a.d.)
Experience shows that there is never a single little change to software, except for fixes and corrections. According to the evolution of requirements, several incremental changes are added to applications, one at a time, leading to different (customized) versions of simulation tools. This development often takes place without any notice or coordination and when the big pile state is reached, a major redesign is inevitable.