In the UK, ordinary families don't have access to large amounts of ready cash - the money they intend to spend on your house is currently tied up in their existing house. So if you want the deepest pool of buyers (& hence to realise the best price for your property) you have to accept being part of a chain of house buyers, all of whom need to perform a dance where they simultaneously sell their houses to each other in order to raise the cash they need to buy the next property in the chain.

It should be unsurprising that this process is widely regarded to be more stressful than anything other than death in the family or divorce.