The reality is a lot more complex.
Taken as a whole, a runic system is referred to as a futhark, a word that is derived from the names of the first six runes (in much the way that the word “alphabet” comes from the first two letters of the Greek alphabet; alpha and beta). What many people don’t realize is that there is no single "correct" futhark, that most of them have a number of runes other than 24, and that the meanings that are commonly attributed to the 24-rune futhark come, in fact, from other futharks that are found much later in history.
The 24-rune futhark with which most Pagans are familiar is called the Elder Futhark. It was used from approximately the 2nd to the 8th centuries CE. However, the order in which the runes are found is not fixed; there are inscriptions of the full runic futhark with either the runes othala or dagaz in the final position. It’s impossible to say definitively which is correct, or even if there is a "correct" ordering. There is also no single correct form for many of the runes of the Elder Futhark, and some that stand for the same rune phonetically have drastically different forms. (Amazingly, no "blank runes" are ever found among those variant forms.)
There are many other futharks, however.
The Anglo-Saxon futhork, for example (it is called a futhork rather than a futhark because the sound of the fourth rune changed from an “a” to an “o”) was used from the 5th to the 11th centuries CE, mostly in Anglo-Saxon England. It, like all futharks, was used for both Christian and Heathen inscriptions. It had anywhere from 29 to 33 runes, and again their forms could vary greatly.
The Viking Age saw the rise of the Younger futhark (9th – 11th century), which was trimmed down to 16 runes (many of the runes doing double-duty phonetically to allow for all the sounds that the language still retained). There were very dramatic differences in the way the Younger futhark runes could be engraved, such as the short-branch and long-twig variations. After that, the 27 Medieval Runes were used through the 15th century, but the order was changed to make them much more in line with the conventional Latin alphabet. There were, of course, many other runic systems in use; these are just the major ones. Some even mixed runic and Latin characters together, and others would be quite unrecognizable as runes to most Pagans (and Heathens, for that matter), such as the "staveless runes" pictured above.
The way the meanings of the runes are known is probably something of which most Pagans are unaware. There exist several runic poems, found in manuscripts from the early to late Medieval period, which present either 33 runes of the Anglo-Saxon futhork or three different variations on the 16 Younger futhark runes.
Notice what we don’t have a poem for? That’s right— the 24 rune Elder futhark. The esoteric meanings that one sees today associated with those 24 runes are lifted from the other rune-poems, usually starting with one of the Younger futhark poems and then filling in the gaps from the Anglo-Saxon rune poem.
The trouble is, each rune poem is a self-contained entity, and advanced runic practitioners can use the meanings encoded into the poems themselves. When they are picked apart, there is a certain level of meaning that is lost. Truth to tell, we simply don’t know what esoteric meaning the runes of the Elder futhark might have had. We can conjecture, but that’s all it is. (As an aside, it should be pointed out that the whole notion that the runes had any esoteric meaning is itself conjecture; many academic runologists maintain that the rune poems are merely mnemonic devices to aid in learning the futharks in a given order, rather than a mystical encoding of their deeper meaning.)
To take one example, consider the first rune in most futharks; fe. Each of the four rune poems gives the following for it:
Abecedarium Nordmannicum: "Feu first"
Icelandic Rune Poem: "Source of discord among kinsmen / and fire of the sea / and path of the serpent."
Norwegian Rune Poem: "Wealth is a source of discord among kinsmen / the wolf lives in the forest."
Anglo-Saxon Rune Poem: "Wealth is a comfort to all men / yet must every man bestow it freely / if he wishes to gain honour in the sight of the Lord."
So is wealth a good thing or a bad thing? A comfort or a source of discord? What’s the significance of the fire of the sea, serpent, and wolf imagery? One can see that among the different poems, there are differences not only in meaning but in associated symbolism.
According to some interpretations of the situation, taking the meanings of the runes out of context (and even out of order, if there is a correct order) is problematical. According to others, one should take an amalgam of all the various interpretations. When even agreement on the fundamental approach for studying the runes can’t be reached, the situation is indeed messy.
Don’t let the messiness of the various futharks fool you, though. There is meaning there, but it is contextual and defies our modern attempts to systematize it for easy consumption. That should not be seen as an excuse to make up meanings of the runes that have nothing to do with any historical notion of their meaning.