The sport of Crossfit is literally the perfect blend between strength and conditioning. Not only do you need to move heavy amounts of weight, you need to be able to do this over long periods of time, sometimes with heavy weights and sometimes with lighter weights or just your body weight (think running/ swimming etc).
For a long time people trained for one or the other. You were either had super high levels of endurance and could go all day or you could lift heavy amounts of weight. The endurance athlete would look thin while the weightlifter may look bigger and bulky.
Blending the two comes at no easy task. If you look at the strength vs endurance continuum, you can see that strength and endurance are non the opposite ends of each other. This makes training for one very difficult to train the other simultaneously.
This is where the fitness Tradeoff comes in. What I have realised and how I now program is that if you look to build one you need to be able to accept that you may only maintain the other or even lose a little, but if you continue to switch them over the course of a year the product of all your results will leave you much further ahead then trying to improve both at the same time.
A lot of competitive crossfitters turn up to their daily session and expect to slowly get both aerobically fitter and stronger throughout the year. This may see their major power lifts go up by 10-20kg for the year with a slight increase in their aerobic base. Not that this does not work, but what if you were able to do two strength cycles in a year, gain 10-20kg on major lifts each time you do it, and then use the other half of the year to focus on conditioning. All of a sudden you have doubled the strength gains and doubled the conditioning gains.
Of course its not just about the two ends of the spectrum, and there is a lot that comes in between but if you program smartly and vary the strength and conditioning programs/ cycles you go through you can cover a lot of ground.
This fitness tradeoff can be hard for some to initially jump into, especially in Crossfit gyms where hard wods and getting out of breath are the norm. But if you allow yourself to go one step backwards in some aspects you will go many steps forward in the long run.