The setting up of a challenge on fast timing to cross the mythic 10 ps frontier on FWHM coincidence time resolution (CTR) for time-of-flight (TOF)-positron emission tomography (PET) scanners (today’s best performance is 214 ps for the Siemens Biograph Vision) is on its way. Inspired by numerous challenges that have had a great impact on human technologies, the rationale for setting up this 10 ps challenge for TOF-PET will be discussed after presenting basics on PET instrumentation and image reconstruction.