It can be problematic. Owners investing thousands, millions maybe, can be highly sensitive to a change of stewardship.
Given such concerns - which tend to be mitigated these days by the issuing of joint licences - rarely can there have been a smoother transition than that between the Hannons - and not merely because the branding of the firm did not have to change when one Richard Hannon succeeded another in 2014.
It has been a remarkable story. When Richard snr relinquished control of his Herridge and East Everleigh Stables near Marlborough at the age of 68 he did so as a four-time champion trainer who boasted five British Classic victories and three in Ireland, and a then record 4,193 wins over a 43-year career - a tally which would only be overtaken by the winner-obsessive Mark Johnston in 2018.
It was a highly distinguished career to follow for Richard jnr, then 38, who for 12 years had been his father's assistant. But having claimed a championship in his first year, he has secured approaching 1,600 victories, including Classic triumphs with Night Of Thunder (2014 2,000 Guineas) and Billesdon Brook (2018 1,000 Guineas).
We speak a few days after he came close to another 2,000 Guineas triumph, with Charlie Appleby's Notable Speech outscoring his Rosallion by one length, with another Hannon contender Haatem, earlier winner of The Craven Stakes, in third place.
Hannon, who believes that this was the best renewal of the Classic for 10 years, is likely to target his pair over different trips once both had contested the Irish equivalent (after we went to press).
"Well, Rosallion, his turn of foot is electric," he enthuses when invited to compare the duo. "Haatem, he goes at it and he breaks horses' hearts. He's got a lovely action and he grinds them down. The further he goes the better he'll be."
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