Even if you have a will, you can be considered as having died with partial intestacy because the will is either contains outdated or invalid provisions, one or more aspects of the will is deemed invalid or illegal, or even if some aspect of your estate is not provided for. If any of these cases are present, your estate will fall into probate, allowing the court to iron out the issues with your will and/or property.
This often happens if an heir named in the will is no longer living, the will has not been updated to reflect more recent assets, or if a will contains questionable or illegal clauses, even those that seem innocent but are not in line with what the law allows. Keeping your will up-to-date and having an attorney ensure its validity is a good way to avoid or reduce the risk of partial intestacy.
All it really takes to avoid this situation, aside from the assistance of a qualified estate planning attorney is to ensure that you review your existing will every few years, updating it to reflect life events, new assets, and provisions reflecting your current wishes. Also, remember that the existence of precedent and subsequent wills can deem a will invalid. To invalidate a previous will, you can instruct your attorney to destroy it, mark through it to void it, or even burn it. Do not let a minor oversight cause you to die intestate, landing your family in a lengthy probate process.