In the aftermath of the Global Financial Crisis, investors appeared to avoid anything that was identified by letters rather than proper words, such as CDO, ABS, RBS, and so on.
It was understandable. Headlines screamed about three-letter debt instruments packaged up by banks that often contained worthless securities - and their holders had no idea until they went "pop".
Against this backdrop, we saw many institutional investors turn to bonds issued by blue-chip companies that, although yielding less than their portfolios would like, were easily identified, explained and measured against competitors.
The blue chips, for their part, were only too happy to oblige - dramatic cuts to interest rates meant they could issue bonds at record low levels.
Over the next decade, issuance soared. By the end of 2017, there was more than $9trn in outstanding corporate debt in the US alone, according to the nation's debt tracking agency. This was more than double the level of just twelve years earlier.
Roll forward to 2019, however, and it appears the sheen of these bond investments has tarnished a little.
The global economy, though jump-started with huge amounts of quantitative easing, has not improved sufficiently for regulators to begin raising interest rates again, despite some tentative steps in the US last year. This means the linked corporate borrowing rate is stuck, too.
Additionally, companies and their advisors soon realised the desire for yield from institutional - and other - investors and began loosening the terms under which they would lend in their own favour.
Combined with these relatively low returns and often relaxed covenants, global regulators have begun to sound the warning bell on the amount of debt that has been issued.
They are also concerned that when rates do start to rise again, a wave of defaults will ensue as so-called zombie companies have been kept on life support for too long.
Add into that concern that due to the looser covenants, any default may come later down the company's life cycle - or when they are further towards the point of 'no return' - and the amount investors might recover from their initial lending could be lower than they expect.