A vicious circle or cycle is when a bad situation feeds on itself to get worse. Many “systems” (social, economic, ecological, technological) are comprised of chains of events that form feedback loops that can under some circumstances reinforce the previous cycle (positive feedback).
It is not uncommon for sustainment-dominated systems (see my January 2017 blog post) to get caught in a “sustainment vicious circle” (or “vicious cycle” ). In this case, more money is going into sustainment (maintaining the systems) at the determent of new investment, which causes the systems to age, which in turn causes more money to be required for sustainment, which leaves less money for new investment, and the cycle continues. The sustainment vicious circle is a reality for militaries of many of the world’s countries, civil infrastructure, and can also appear for systems owned by individuals. For example, individuals might face this dilemma with their automobile – fixing your existing car is expensive, but it is less expensive than buying a new car; after several such repairs one is left to wonder if purchasing a new car would have been less expensive, but there is no turning back, too much has been invested in repairing the old car (the funds that could have been used to purchase a new car have been spent).
Setting aside your used car, in this blog we are primarily talking about large, complex, expensive systems, like a fleet of aircraft, a fleet of buses, rail infrastructure, the water/sewer system in cities, etc. These things are massively expensive to replace or upgrade (and massively expensive to sustain). Let’s be clear, not every large, complex, expensive system suffers the sustainment vicious circle – many are well managed and correctly funded. However, the evidence of sustainment vicious circles are all around you – look at the neglected portion of a city’s aging infrastructure. The cause of the sustainment vicious circle is often the inability or unwillingness of system’s owners (which may be the public) to budget appropriately for sustainment (operation and maintenance), which is exacerbated by unanticipated life extensions of the system requiring it to last longer than it was designed (or funded) to last. The money to build new things is always easier to get than the money to sustain old things AND old things always end up having to be supported longer than anyone anticipated.
How do you get out of a sustainment vicious circle? Either the system reaches its breaking point (literally, possibly catastrophically) and simply must be replaced, or the system has to be transitioned to a more “vital cycle” that would reduce the sustainment costs of legacy systems, and provide for modernization. Pursuing the “vital cycle” is not cheap (customers have to be willing to pay) and it usually comes with one key caveat: any action taken cannot adversely affect the customer’s needs in the short term.
Corollary to the Vicious Circle – The Upgrade Trap 
Related to the vicious circle is the “upgrade trap”. A common version of the “upgrade trap” is forced upon consumer electronics users. How often have you been forced to buy a new device because none of your software would run on your old hardware? The upgrade trap is indiscriminant, even users that derive no actually benefit from higher-performance hardware or greater functionality software, are forced to “keep up” whether they want to or not. Even systems that are seemingly disconnected from commercial interests such as military systems are impacted, e.g., if these systems contain COTS (Commercial Off-The-Shelf) application software, the continued support of the application may require hardware upgrades that are not otherwise needed or wanted. Is the upgrade trap by design – certainly, it is a form for planned obsolescence (see my February 2017 blog post).
The one thing that is worse than being caught in the upgrade trap, is not being caught in the upgrade trap, i.e., being caught in the “sustainment vicious circle”.
 Achieving an Innovative Support Structure for 21st Century, PSB 96 (10-13-97)
 Sustainment, Proceedings of the Sustainment Team of the Industry Affordability Task Force, Report Number 98-SS1A, National Center for Advanced Technologies, January 1999 http://www.ncat.com/sustain.pdf
 P. Sandborn and J. Myers, "Designing Engineering Systems for Sustainment," Handbook of Performability Engineering, ed. K.B. Misra, Springer, pp. 81-103, London, 2008.