Nick Chester, the technical boss at Renault, says he sympathises with Williams.
Embarrassed team boss Claire Williams apologised to the team's fans and drivers last week following a more than two day delay for its new 2019 car.
But only a week earlier, boss Cyril Abiteboul had also warned that Renault also came close to a delayed start at the first Barcelona test.
Chester explained: "If you have not been involved in the production of formula one cars, you do not know how difficult it really is.
"Within a week or two we are talking about thousands of parts. And they all come at once," he is quoted by Speed Week.
"One or two problems are enough to be four to five days late. It's a daunting task," Chester added.
He said Williams will now be working to "trim" its programme and prioritise tasks that are less important.
"The problem with that is that you really do need every kilometre for reliability and to understand the car. The missed days just hurt," said Chester.
