Some could say that reliability of SSDs is less than magnetic HDs but that is debatable. First, is the number of write cycles - or truly sector-erase cycles, in the case of flash memory because erasing a sector is when danage can be done to the memory. SSDs can usually do 100,000 erase cycles (at room temperature) before excessively slowing down, which equates to 300 years writing to each disk sector once a day, this reduces to 10,000 cycles at high temperatures (usually internal temperature of 85°C) but still this is 30 years at one erase per sector per day. This is nothing compared with HDs which can do approximately 1,000,000 write cycles, hence why some say they don't degrade. Obviously they do; a well used HD could start having block failures after five years and it is common for the control hardware to fail before the magnetic disk!
What is more interesting is shelf life. A hard disk could probably survive 30 years or more in cold storage, but eventually the magnetic coating of the platters will degrade, losing their magnetism and the data with it. Conversely, the floating gates in flash memory could hold their charge indefinitely, in theory. That's forever folks! Plenty long enough for anyone! I say in theory because we're now entering the world of quantum mechanics where there is a small possibility that the electrons in the charge "exist" outside of the floating gates and therefore could leak out eventually. However this probability is so small - and the number electrons so large - that leaking the odd electron over millennia would have no noticeable affect. The disks will be long lost and buried by the time the data are lost! Panic over!
The third thing to note is the problem of rapidly changing data. Most rapidly changing data resides in RAM of course. But caches, such as RAM disks (a file on disk that acts like RAM) or virtual memory (a cache that is used to extend the size of RAM that programs believe they have access to, used to swap pages in and out of RAM, which is why it's also referred to as a swap file), have far more writes than once per day. These are typically the areas that wear out first, explaining why HD life expectancies reduce from 3,000 years to 5! Flash memories have a cunning plan so that these areas of memory don't die in six months: they swap sectors around. For each sector a sector erasure count is recorded. The flash controller should pick the next empty (or marked for erasure) sector with the lowest erasure count to write to. For example, if a cache occupies just one sector and there are 100 sectors free on the disk, the controller should ensure that each sector is used equally, thereby reducing the wear on each by a factor of 100. So, if the cache is written to 100 times a day the life expectancy of these sectors would still be 300 years. If the access rate is higher the life expectancy decreases; 1000 times a day is 30 years, 10,000 is 3 years and so forth. But what typically happens on a hard disk is one set of sectors gets written to and never changes while another set is constantly changing. HDs just keep the unchanging block in the same location because they are so slow (unless you defragment the disk, which may move permanent blocks of memory) whereas SSDs can swap around unchanging sectors with rapidly changing ones. For example (note I do not know the actual algorithms but this will serve as an example) if the controller realises one sector has been erased 100 times but it knows there are plenty of sectors that have never been erased - that hold "permanent" data - it can erase the overused sector, copy the data from the underused sector, erase that and now a sector with an erase count of just 1 is available for a cache. By recycling sectors that contain "permanent" data the wear of the SSD can be evenly spread reducing the average sector erasure rate back down to 1 erase per day and increasing the life expectancy to 300 years! So, all things being equal - which as I have shown they are definitely not - SSDs are probably more robust and reliable than magnetic HDs. Remember: don't panic! Usually some bright engineer has worked out the problems and implemented solutions before you even knew they existed; new technology is real progress rather than change for change's sake. (Unlike politicians...)