Many promises are made at the altar during a merger or an acquisition. Most of them get broken. It is worth reminding yourself of this now, before the next wave of whirlwind corporate romances arrives.

So far this year there has been only mixed evidence of renewed appetite for M&A. Sure, the proposed £40bn ($66bn, €47bn) merger between the mining companies Xstrata and Anglo American caught the eye, just as Oracle’s $7.4bn deal to buy Sun Microsystems and GlaxoSmithKline’s $3.6bn move for Stiefel Laboratories did.