One of the things sportsmen often say when they are talking about the strength of team spirit is that "we are like brothers". It's the phrase they use when they mean they couldn't get any closer to the people they play alongside.
But when there actually are brothers in the team? I suspect it is a slightly different matter. Be honest with yourself, all that sibling rivalry, the thought that one or the other got better treatment from your parents, more chances, better Christmas and birthday presents, it never quite goes away, does it?
For instance Bobby and Jackie Charlton might have been two lynchpins of England's immortal 1966 World Cup winning team, but they famously didn't talk to each other for years. Phil and Gary Neville appear to get on great, but watch their Twitter feeds and you can see the little bits of rivalry surface now and then.
Which brings us to Andy and Jamie Murray, who seem to have a similar mix of close family bond combined with a tinge of mutual envy. Andy's admitted in the past that he was driven as a kid growing up in Dunblaine by trying to keep up with his elder brother. Yet it is Jamie who is now in the shade of a former Wimbledon champion and current world number five.
If anybody wanted to study the psychology of these things there would be no better place than Glasgow this weekend. Britain face America in a first round Davis Cup tie, and the pivotal match will be one set of brothers against another.
The Murrays don't often play doubles together. Andy has admitted he hates the pressure if they team up in a tour tournament of knowing if they go out first round he'll have ruined Jamie's chances of making any money that week.
When they do they are not a bad team - but they aren't in the same class as Bob and Mike Bryan who they will have to face in the match which may well decide the tie.
The Davis Cup heaps huge pressure on Andy. Basically he is a one man team for Britain at this level. He has to beat World number 47 Donald Young and then the towering 6ft 10ins John Isner in his two singles matches. That will be demanding enough, but he must then try to share a doubles victory with Jamie in the middle of it all.
He'll have the help of a hugely patriotic home crowd, but that seems to me to be such a tall order that I can't understand why Great Britain are as short as 1.824/5 favourites to win the tie.
There's no doubting Andy's passion for playing. He caused a stir by supporting Scottish independence before the referendum last year, but when it comes to appearing for Great Britain alongside his brother he'll be flying the flag with the best of them.
The problem is that while there are those little tensions on his side of the net, on the other side the Bryan Brothers really are - well, like brothers. In Davis Cup ties their record is 23 victories against just four defeats. It's only a couple of weeks ago they won the Delray Beach Open to collect their 104th title as a team out of 155 doubles finals.
Britain beat the USA the last time they met in Davis Cup, but that was on clay and with Isner unfit. This time it just looks too big an ask, and if you don't have any scruples about betting against your own country then up to 2.226/5 for an American win is just too good to miss.