Yes Jasper I'd hope you were right, but it never starts like this. What often happens is that just as when we might meet a new female friend with whom we really hit it off, there is almost a process of falling in love with that friend. New friends often search for areas of commonality and go through a process of "mirroring" to achieve that common ground.
Male/female friendships are often no different, especially if there is an added professional benefit to achieving a collaborative working relationship where targets are reached. However, if there is an unexpressed physical chemistry present, this injects an extra frisson to the relationship. However this isn't regarded as dangerous either, because of course it is culturally sanctioned that we will find others attractive even if we are in a committed relationship.
Inevitably too, that friendship might lead to exchanges of information about one's personal lives. After a while, one of them might report unhappiness at home and marital discord. The happier friend doesn't want to gloat about their better relationship, so either keeps quiet or once again, finds areas of commonality and discloses either minor or entirely fictitious marital grievances of their own.
If they start to keep in touch outside of work via texting, E mails or messenger services, at some point they start to synchronise the best times to do so "in case their spouses get the wrong idea." Hence, a level of secrecy has entered the relationship.
The delusions people have throughout these early days of a new friendship are obvious to see, with hindsight, but at the time, one or both of the parties would still insist that this friendship was safe and unthreatening.
Every step taken, every barrier broken serves to normalise the last, because this often happens over a long period of time and it becomes the new "norm."
Hence, the stage when both friends confess their mutual attraction doesn't seem like the watershed moment it represents, because that now feels perfectly normal and acceptable. The next step is a kiss and on it goes until a full affair is underway.
How many women do we see on here who say "I don't know how it happened, I got carried away" Or "Before I knew it, I was having an affair..." as though they have been captured by aliens or dark forces? It happened because they ignored the boundaries and took all the incremental steps detailed above.